An electromagnetic actuator that drives the drive unit of a valve is described in Japanese Patent Laid-Open Publication No. 7-224624. The drive unit is driven using an electromagnetic force. The electromagnetic actuator detects a change in the position of the drive unit based on the change in self inductance of an electromagnetic coil.
In the conventional electromagnetic actuator, an oscillating circuit is used to detect the self impedance. This oscillating circuit changes the frequency of oscillation based on the change in the self impedance. As a result, there is a drawback in that it takes a lot of time for the detection of the self impedance depending upon the frequency of oscillation of the oscillating circuit. Also, in the conventional electromagnetic actuator, apart from the oscillating circuit, a rectifying circuit is also required. Thus, there are disadvantages with the conventional electromagnetic actuator in that it has a complex configuration and high cost.
It is an object of the present invention to provide an electromagnetic actuator, a valve drive unit, and a position or speed sensor that detects the speed and the change in position of the drive unit accurately and with simple configuration. It is also an object of the present invention to provide a valve drive unit and a position or speed sensor employing the electromagnetic actuator.